LONDON (Reuters) - Dominic Thiem offered a further pointer to a future world order in men's tennis as the Austrian briefly ruffled Novak Djokovic's feathers on his ATP World Tour Finals debut on Sunday.

The 23-year-old, the first Austrian to finish in the top 10 since Thomas Muster in 1997, produced some electrifying moments during a first-set tiebreaker that he snatched 12-10.

Although his challenge fizzled out thereafter, some of his play -- especially a sweet single-handed backhand -- had a sell-out O2 Arena crowd roaring its approval.

Not that they should have been surprised. After all world number nine Thiem has won four titles this year and reached the semi-finals of the French Open where he also lost to Djokovic.

World number two Djokovic was impressed as he dropped a set to the Austrian for the first time in four meetings.

"Dominic definitely seemed very impressive considering it was his debut in the World Tour Finals," Djokovic said.

"It didn't seem like he was overwhelmed by the stage or occasion. He came out firing. He came out really playing great tennis. Got to give him credit for that. He was obviously very pumped up to get to the court and give his best."

While Djokovic and new world number one Andy Murray look set to dominate in 2017, the likes of Thiem, Germany's Alex Zverev, Australian Nick Kyrgios and several others are beginning to make inroads into the top echelons of the game.

Thiem will be disappointed that his challenge faded so quickly, but with matches to come against fellow debutant Gael Monfils and Milos Raonic all is not lost.

"It was a really good atmosphere. I mean, 17,000, it's I think by far the biggest crowd I ever played in front of," Thiem said. "I think they are also excited to see some new faces at this tournament. That's why they cheered a lot for me I guess.

"If I keep the level from the first set, it's not a guarantee that I win the match, but I have chances.

"I want to play two more good matches, then I will see what the outcome is. But first of all, it's a very good experience for me to play three matches against top-10 players."

Djokovic, who saved six set points, two with the help of Thiem double faults, in the first set, coasted through the first nine games of the match before things got tricky.

While frustrated at losing the opening set, the 29-year-old said he was pleased with his performance as he targets a return to the ATP top ranking before the end of the year.

"I didn't manage to win that first set, of course you're frustrated. On the other hand, I think I managed to kind of compose myself and really gather all my attention and concentration to what was coming up after that," he said.